The central hypothesis for this application is that Alzheimer's disease (AD) is a multi-factorial disorder in which a number of agents, including environmental determinants, contribute to a disparity between amyloid beta (Abeta) - production and Abeta clearance. This disparity leads to the accumulation and subsequent deposition of Abeta peptides that eventuates in the neuropathological presentation of AD. Based on this hypothesis, numerous laboratories have emphasized the biological aspects of amyloid precursor protein (APP) synthesis and metabolism and the mechanisms of Abeta production in AD. However, the molecular mechanisms of Abeta overproduction appear to contribute to only a portion of the total AD cases. The nature of Abeta degradation and clearance is the least studied mechanism in the process of AD progression and it is a likely target for therapeutic intervention. Recent studies indicate that the neutral endopeptidase neprilysin plays an important role in the degradation of Abeta(1-42) in the brain. The Specific Aims of this proposal are: 1) to provide evidence that NEP can regulate Abeta levels and deposition in vivo, which will be done by crossing transgenic mice overexpressing NEP or NEP-deficient mice with APP transgenic mice and assessing progeny biochemically and pathologically; 2) to use a cell-based system to study the susceptibility of NEP to oxidative damage; and 3) to compare NEP levels/activity in human AD brain and age-matched controls and to determine whether oxidative damage contributes to altered NEP activities. These studies will help determine how Abeta is degraded extracellularly, whether NEP plays a key role in this process, and how Abeta levels are regulated by the activity of NEP. The results generated from this study will help us to understand how Abeta peptides are degraded and may provide a unique therapeutic window for the treatment of AD.